Please be careful not to mix up several similar, but potential=
ly different
issues.

First of all, any PRIME functionality requires that acceleration is
successfully initialized for all GPUs involved, otherwise the X server will
crash when trying to use it (which is unfortunate, but the way it is right
now).

In Adam's case, acceleration failed to initialize for the discrete GPU with

 (EE) RADEON(G0): Failed to create EGL context
 (EE) RADEON(G0): glamor detected, failed to initialize EGL.

If this still happens with current Mesa Git, setting the environment variab=
le
EGL_LOG_LEVEL=3Ddebug for the Xorg process should give more information abo=
ut the
failure.

In Vitaliy's case, the problem is the lack of glamor support in Debian sid.
This is fixed in the X packages in Debian experimental.

dimitris says glamor initializes successfully for him, so it's probably a
different problem which should be tracked in a different report.